Fair Value Of Financial Instruments (Aggregate Fair Value And Remaining Contractual Principal Balance Outstanding On Fair Value Option) (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Residential Mortgage Loans [Member] | Loans Receivable [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable and other instruments, contractual outstanding principal	$ 40	$ 89
Loans receivable and other instruments, 90 days or more past due, contractual outstanding principal	138	147
Loans receivable and other instruments, fair value	40	89
Loans receivable and other instruments, 90 days or more past due, fair value	37	31
Loans receivable and other instruments, difference	0	0
Loans receivable and other instruments, 90 days or more past due, difference	101	116
Total Loans Receivable and Other Instruments [Member] | Loans Receivable [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable and other instruments, contractual outstanding principal	178	236
Loans receivable and other instruments, fair value	77	120
Loans receivable and other instruments, difference	101	116
Variable Interest Entity Notes [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Long-term debt instruments, contractual outstanding principal	918	1,117
Long-term debt instruments, fair value	292	350
Long-term debt instruments, difference	626	767
Medium Term Notes [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Long-term debt instruments, contractual outstanding principal	116	122
Long-term debt instruments, fair value	102	110
Long-term debt instruments, difference	$ 14	$ 12